(2) Reactivate the OWS in Earth orbit. Operate the orbital assembly (OWS plus command and service module) as a habitable space structure for a period of 56 days, with the option of extending to 84 days after the third-visit launch. Obtain data for evaluating the performance of the orbital assembly. Obtain data for evaluating crew mobility and work capability in both intravehicular and extravehicular activity.

(3) Obtain medical data on the crew for use in extending the duration of manned space flights. Obtain medical data for determining the effects on the crew which result from a nominal space flight duration of 56 days, with the option of extending to 84 days. Obtain medical data for determining if a subsequent manned space flight mission of greater duration than the duration of the Skylab third manned visit is feasible and advisable.

Although not a primary mission objective, a requirement to obtain documentary motion picture photography of scenes to present the human story of Skylab was considered to be of paramount importance. Approximately 95 percent of the desired crew activity scenes were filmed.

The planned requirements were not only met, but were exceeded for almost all experiments. Also noteworthy were the large number of candidate experiments that were performed. There were 70 telecasts during the third visit. Premission planning for this visit made provisions for the development of telecast requirements which would be timely and would not be a repeat of subjects covered during the earlier two visits.

This planning included three flight-data-file 'TV Numbers' which were for television on a variety of subjects. These numbers were TV-77, general purpose intravehicular activity telecast; TV-78, Earth surface features; and TV-81 optional crew day- off activities.

The following conclusions were based on Skylab 4 activities.

(1) Crew refresher exercises in spacecraft operational modes and procedures were needed during long missions.

(2) Free and open discussions between the crew and the ground were necessary for the expeditious resolution of sensitive issues. When one party felt that the other was at fault, the existence of a routine private communications loop, less restricted use of existing capabilities for special private conferences, or less reluctance on the part of the crew and the ground to use the open communications loop to critically discuss sensitive subjects would expedite the solution of problems.